Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Q-Jet 17057274 idles too fast
TommyK:
I don't think you ever stated what your initial timing is. Have you checked the timing pointer position by placing the #1 piston on TDC and verifying 0 on the balancer?
beertracker:
Ignition base timing is set to 12 deg. BTDC. It's a Pontiac 400 and on a Pontiac forum I was told to set it to 12 deg. I can change it to 0 deg and see what happens. bt
TommyK:
Reducing the timing will almost certainly change the idle speed. The question is whether or not the 12 degrees you are reading on the balancer is actually 12 degrees. If you would take a few moments to pop the spark plug out, get the no. 1 piston as close as you reasonably can to TDC on the compression stroke and verify 0 on the balance it will either at best uncover a potential cause of your high idle or at least eliminate one variable from the equation.
Shark Racer:
--- Quote from: beertracker on January 07, 2013, 02:13:46 PM ---Forgot to mention the carb is drilled for by pass air. bt
--- End quote ---
How much bypass air is there in the baseplate? This could very well be the cause if you went hog wild on it.
beertracker:
--- Quote from: TommyK on January 07, 2013, 02:32:42 PM ---I don't think you ever stated what your initial timing is. Have you checked the timing pointer position by placing the #1 piston on TDC and verifying 0 on the balancer?
--- End quote ---
Yes, just performed this step and the timing pointer is at 0 on the balancer with #1 piston at TDC compression. I also slowed dist timing down to 0 and the rpm dropped by 25 to 1275 rpm. Very insignifiicant.
Since my hot air choke isn't working I blocked off the air passage between the choke housing and carburetor. This made the engine harder to start, backfire out the tailpipe once and through the carburetor once. After the engine warmed up it was idling too fast just like before. I plan to back this change out.
I was wrong about my base plate being drilled for bypass air, it's not. Does my problem seem like it could be solved by adding bypass air? I haven't ruled out a vacuum leak causing this problem. Or what should my next step be?
In Cliff's book he talks about how to install idle bypass air and modifying the idle system. Should these be done seperately or can they be done at the same time? If they are done seperately they can be tested individually before moving to the next one.
bt
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